Cast graphitic nickel alloy and method of making same



pt. 8 1 1 G. L. LEE Em 2,568,013

CAST GRAPHITIC NICKEL ALLOY AND METHOD OF MAKING SAME Filed March 2'7, 1948 62-52910 [INF/20 155 INVENTORS Patented Sept. 18, 1951 CAST GRAPHITIC NICKEL ALLOY AND METHOD OF MAKING SAME Gerald Linfield Lee, Plainfield, and John Trimblc Eash, Westfield, N. J., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application March 27, 1948, Serial No. 17,446

11 Claims.

The present invention relates to nickel alloys and, more particularly, to an improved nickel casting alloy having an unusual combination of properties including castability, machinability, high strength, improved ductility and toughnessv and high resistance to galling and wear; and to castings made therefrom.

It is an object of the present invention to provide a nickel casting alloy having high strength, ductility and toughness, in combination with good castability and good machinability.

It is a further object of the present invention to provide an improved nickel casting alloy having high strength and toughness, together with improved fatigue resistance.

It is a still further object of the present invention to provide an improved nickel casting alloy having a high combination of strength, ductility and toughness, together with improved resistance to falling and wear.

It is another object of the present invention to provide improved articles made from a nickel casting alloy, for example, pressure tight castings having high strength and ductility, which can be easily machined and which will take a good machined finish or can be ground and polished readily.

. Other objects and advantages of the invention will become apparent to those skilled in the art from the following description, taken in conjunction with the attached drawing in which Figure 1 is a reproduction of a photomicrograph taken at 500 diameters showing the flake graphite structure which characterizes a nickel-carbon alloy base composition devoid of the special addition element contemplated by the invention and Fig. 2 is a reproduction of a photomicrograph taken at 500 diameters showing the nodular graphite structure of an alloy containing a preferred amount of the special addition element contemplated by the invention.

Broadly stated, the alloy of the invention is a graphitic nickel alloy containing at least 0.8% and up to about 3% carbon and at least 0.035% up to about 0.45% of magnesium in excess of that required to combine with sulfur. The alloy will contain at least about 0.08% up to about 0.45% combined carbon, while the remainder of the carbon will be present in an uncombined or graphitic form. Silicon and manganese are desired constituents which promote fluidity and improve castability and are present in amounts of from about 1% to about 4% and of from about 0.5% to about 4%, respectively. The alloy may be devoid of iron or may contain up to about of iron,

e. g., about 0.1% to about 10% iron. The balance of the composition is essentially all nickel with the exception of small amounts of incidental impurities characteristic of nickel casting alloys and present as a result of the raw materials employed in making the alloy, the apparatus, deoxidation and/or malleabilization treatments, and other treatments employed to produce commercially acceptable products.

An important effect attributable to magnesium in the alloy of the invention is that of causing the graphite to occur in the nodular form. However, in order that the magnesium content of the alloy be effective in exercising this control over graphite occurrence, it is essential that the amounts of magnesium specified herein be in excess of the amount of magnesium required to react with and fix any sulfur present in the alloy.

Those skilled in the art know that magnesium and sulfur can be co-present in nickel and it has been considered that these elements react in nickel to form a magnesium sulfide. For practical purposes, and for purposes of the present invention, it has been found that about one part by weight of magnesium retained in the alloy of the invention may be considered to be consumed in fixing each part by weight of the sulfur present in the alloy, and that only the excess of retained magnesium above this amount is capable of causing the graphite to occur in the nodular form. For exampleyone graphitic nickel alloy containing 1.25% carbon and 2% silicon had all the graphite present in the flake form when 0.047% of magnesium was present along with 0.075% of sulfur. In another instance, substantially all the graphite was in the flake form when 0.066% of magnesium was co-present with 0.037% of sulfur in the same base alloy as the previous example, and, in still another instance, it was found that 0.11% of magnesium was insuflicient to cause all the graphite to occur in the nodular form when 0.074% of sulfur was present in an alloy having the same base composition as the foregoing. On the practical basis that one part of magnesium is required to neutralize each part of sulfur in the alloy, it can be said that in order to cause graphite to occur in the nodular form the retained magnesium content should exceed the sulfur content by 0.035% to 0.45%.

Alloys having compositions within the foregoing ranges are characterized by a microstructure in which at least about 25% of the graphite appears in the nodular form, and when the excess retained magnesium exceeds about 0.045% substantially all the graphite appears in the nodular form. In addition, when the excess retained magnesium exceeds about 0.035%, a clear white excess phase or beta phase, which is believed to be a nickel-carbon-magnesium eutectic phase, is present. The amount of this excess phase increases as the excess retained magnesium content increases. The flake graphite form found in graphitic nickel alloys devoid of magnesium is depicted in Fig. 1, while the characteristic nodular graphite form and the excess white phase present in graphitic nickel alloys containing preferred amounts of magnesium contemplated by the present invention are depicted in Fig. 2. The graphite nodules are randomly distributed throughout the matrix, while the excess white phase, or beta phase, tends to appear in a dendritic pattern. The raphite nodules will vary in size, some besired to provide alloys having high strength combined with an elongation of 25% or more, alloys having carbon contents within the range of about 1% to about 2% in combination with excess retained magnesium contents between about 0.06% and 0.11%, with the balance of the alloy being nickel and elements within the ranges set forth in Table I, should be employed.

In order that those skilled in the art may have a better understanding of the present invention, examples illustrating the analyses of preferred alloy compositions and resulting physical properies, together with comparative examples illustrating the effect of variations in composition. are given in Tables 11 and III. The balance of the compositions in Table II is essentially nickel.

The composition may be devoid of iron, or may contain up to about 10% of iron, e. g., about 0.1% to 10% iron, and the balance of the composition is essentially all nickel.

Compositions within the ranges defined in Table I will have high strength as indicated hereinbefore and will have elongations of at least 15%. When elongations of or more are desired, the excess retained magnesium should be maintained within the range of about 0.04% to about 0.17%, with the balance of the composition bein substantially all nickel and elements within the ranges defined in Table I. It is preferred that the excess retained magnesium content increase as the carbon content increases. Particularly satisfactory combinations of properties were obtained in nickel alloys containing silicon and manganese within the ranges of Table I and which contained 0.045% of magnesium in combination with 1% of carbon, 0.09% of magnesium in combination with 2% of carbon and 0.17% of magnesium in combination with 2.5% of carbon.

In the compositioins falling within the ranges set forth hereinbefore, e. g., the alloys containing 0.8% to 3% carbon and the preferred alloys containing 1% to 2.5% carbon, it is preferred that the excess retained magnesium content be at least 0.06% of the alloy and it is more preferred that the excess retained magnesium content be within the range of 0.06% to 0.11%. When it 18 (IQ- ing larger and some being smaller than those Table H shown in Fig. 2. These nodules may have a welldefined radial rosette pattern or may occur as go Pergeni Persciient Pe c ent rounded chunks.

Alloys within the foregoing ranges of composi- 90 063 2 31 1 32 tion will have tensile strengths of at least 50,000 1 pounds per square inch along with good ductility. {3 g; 1% In order to obtain this high strength, it is critical .90 I31 1194 Zoo that the composition be kept within the ranges g A fi 45 defined hereinbefore, particularly with respect to the magnesium. If tensile strengths on the order of 55,000 pounds per square inch are desired, a Table III range of excess retained magnesium contents be- 30 tween about 0.04% and about 0.4 should be emem ployed, with the balance of the composition be- 5 B a gg; BHN ing as hereinbefore defined. m

Preferably speaking, the compos ons employed according to the invention are those set Egg Egg f; -3 5g forth in Table I. g g g :23 f5 (1% fig Table I 241400 391700 1 6 101 Element Percent assessments;.s'sslassraaisai'ia 'I. S.-Tensile strength, pounds per square inch. l-2. 5 Per Cent EL-Peroent of elongation in two in h s, 0. 035-0. 25 Clgr py impact-Impact resistance in foot pounds. 1. 5-2 0 B -BrineII hardness number. Manganese 1l.5 n. d.-Not determined.

Tables II and III illustrate that the magnesium-containing graphitic-nickel product of the invention possesses a greatly improved combination of strength and ductility, especially when compared with a magnesium-free graphitic nickel alloy of essentially the same base composition but which contains graphite in flake form, e. g., No. '1 in the table. No. 5 illustrates the fact that the elongation is reduced when magnesium is present in amounts greater than the preferred amounts, although the strength values remain at a high level. In No. 6, when the magnesium content was increased to an amount greater than that contemplated by the invention, the resulting melt was very sluggish and could not be poured to make a sound casting.

As indicated hereinbefore, alloys having compositions within the ranges contemplated by the invention have excellent casting properties and may readily be cast to produce pressure-tight castings. In addition, these castings can be machined, e. g., subjected to threading operations, etc., at feeds and speeds customarily used for machining gray cast iron and an excellent machined finish is produced. Alloys having compositions within those contemplated by the invention have also been found to have high resistance to galling and wear both in laboratory tests and in feld tests, when the carbon content is at least about 2%, e. g., 2% to 2.5% or more. For examp p on ring ma e of the preferred alloy of the invention and of a comparable magnesiumfree graphitic nickel alloy containing graphite in the flake form were subjected to an engine test in the type of equipment used in testing aircraft engine piston rings. Piston rings made from the alloy of the invention showed greatly improved resistance to galling and wear under these conditions as compared to piston rings made from a comparable magnesium-free alloy.

In addition to the foregoing, it has been found that the fatigue strength of the preferred alloy of the invention determined on smooth R. R. Moore rotating beam specimens was about 20,000 p. s .i. at cycles, while, in the same type of test, the fatigue strength of a comparable magnesium-free alloy was found to be 14,000 p. s. i. at 10 cycles.

The alloys of the invention are characterized by high toughness in combination with the high strength, ductility and improved fatigue resistance described hereinbefore. In the standard Charpy impact test, the alloys of the invention have an impact resistance of 25-34 foot pounds whereas similar magnesium-free alloys have an impact resistance of only about 10 foot pounds.

As pointed out hereinbefore, a distinctive feature of the microstructure of the alloy of the invention is the presence of nodular graphite in the microstructure. Although it has been found that nodular graphite may appear in the microstructure of graphitic nickel alloys which are free of silicon, no prior art process, as far as is known, has provided a graphitic nickel alloy containing nodular graphite in the co-presence of the amounts of silicon employed in the present invention. Silicon tends to cause graphite to occur in the flake form.

It is to be pointed out that certain elements interfere with or may even prevent the formation of nodular graphite in the alloy of the invention. For example, it has been found that titanium and zirconium have such an efiect. The amounts of these subversive elements contained in the alloy should be restricted to a maximum of about 0.3%, e. g., 0.01% to 0.3%. The total content of titanium and zirconium should not exceed about 0.5%. Columbium and aluminumalso have an interfering tendency, although not as strong as that of titanium and zirconium, and these elements should not be present in amounts greater than about 0.75%, e. g., 0.01% to 0.75%, and the total amount of these two elements should not exceed about 1%. Amounts of lead up to about 1% reduce the ductility but have no deleterious effect otherwise. It is preferred that the alloy be free of lead but this element may be present in amounts of about 0.01% to about 1%.

Other elements which may be present as minor constituents and/or impurities include cobalt, copper, chromium, zinc, etc. The alloy may be devoid of any of these minor constituents and/or impurities or it may include amounts of cobalt from about 0.1% up to about 5%, of copper from about 0.1% up to about 8%, of chromium from about 0.1% up to about 5%, and of zinc from about 0.1% up to about 3%. It is to be under stood that when nickel is said to constitute the balance" or when it is said that the balance is substantially all nickel or essentially all nickel or essentially nickel, it is not intended to exclude minor constituents and impurities which may be present in the amounts which occur in comparable nickel products, or in amounts not adversely affecting the desired properties of the alloy.

. As pointed out hereinbefore, distinctive features of the microstructure of alloys within the invention arethe presence of a randomly distributed graphite excess phase having-a nodular structure and the presence of another excess white phase or beta phase having a, eutectic structure which tends to appear in a dendritic pattern. The relative amounts of this excess white phase appearing in the microstructure of the cast alloy are largely a function of the chemical composition of the alloy. The excess white phase or beta phase increases in amount with increases in the magnesium content of the alloy. It has been found that any increases in the magnesium content tend to increase the combined carbon content and decrease the uncombined or graphitic carbon content of the alloy, and in the preferred alloys of the invention, the combined carbon content will be within the range of from about 0.15% to about 0.35%. Increases in the magnesium content tend to increase the ratio of combined carbon to graphite or uncombined carbon in the alloy. Some of the combined carbon seems to occur as a componentof the beta phase which apparently contains magnesium, carbon and nickel. Since the occurrence of graphite in a nodular form isa property conferred by a cooperative'efiect of the magnesium and carbon contents of the alloy, the amount of nodular graphite appearing in the structure is directly proportional to the uncombined, carbon content of the alloy when magnesium is present in preferred amounts. It is believed that the microstructure contributes importantly to the unique combination of properties possessed by the alloy.

The alloy of the invention can be produced in any of the furnaces normally used for melting nickel alloys, e. g., the direct arc furnace, induction furnace, crucible furnace, etc. A convenient method which may be employed in melting the alloy is to first prepare a nickel melting stock containing 2% .or more of carbon. This melting stock can then be remelted and diluted, if necessary, with nickel (e. g., electronickel) to produce the desired carbon content in the solidified alloy. In this manner, good control. of carbon content can be effected. The manganese, silicon and magnesium additions can then be introduced in any suitable manner.

A beneficial practice which has been developed for handling molten nickel-carbon .melts from which the alloy of the invention is to be made comprises adding the manganese and half of the desired silicon after the melt-down has been completed and the temperature of the melt is suitable for casting, e. g., about 2450 F. to about 2750 F., making the other desired additions to the melt including the magnesium addition, and then adding the remaining half of the silicon as the final addition before casting. It has been found that this practice removes any scum which may form on the surface of the melt following the manganese or magnesium additions and contributes to the production of sound castings. It is preferred that the final silicon addition be at least 0.25% of the alloy, e. g., 0.25% to.2 .5,%, preferably 0.5% to 1%. As described hereinbefore, it has been found that, as a good practical expedient, the final silicon addition can be about half of the total silicon addition desired. As those skilled in the art know, silicon may be added to nickel melts in the form of an alloy with iron containing 50% to about 97% silicon, for example, 97% silicon and manganese may be added in the form of an alloy with iron containing 60% to about 97% manganese, for example, 97% manganese. Magnesium may be added as an alloy with nickel, for example, a 67% magnesium-33% nickel alloy, or may even be added as metallic magnesium. As in casting all high nickel alloys, risers and gates should be generous and a shrinkage allowance of about inch per foot should be made. Of course, the

.moisture content of the molding sand should be carefully controlled and, if oil bonded cores are used, they should be completely baked and dried, otherwise some difiiculties may be encountered which may produce porosity, etc., as a result of a reaction between the molten metal and the sand mold and/or sand core.

The alloy of the invention possesses a unique combination of properties which make it useful in a wide number of applications. Thus, the alloy of the invention has excellent foundry characteristics, i. e., it has good fluidity in the molten state, fills the mold sharply when cast, and has little tendency toward the production of internal voids and shrinkage cavities, provided proper mold design is employed. Thus, castings which have to be pressure-tight may safely be made from the alloy of the invention. Castings of the alloy are readily machinable and have high strength combined with good ductility and impact resistance. In addition, articles made from a high carbon alloy possess high resistance to galling and wear.

The unusual combination of properties possessed by the alloy make it suitable for use in the form of castings in a wide variety of applications such as liners, bushings, heavy duty bearings, pump housings, impellers, hydraulic valves, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to Without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Variations and modifications apparent to those skilled in the art are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A graphitic nickel alloy containing 1% to 2% carbon, 1.5% to 2% silicon, 1% to 1.5% manganese, sulfur up to 0.08%, magnesium in an amount exceeding the amount of sulfur present by 0.06% to 0.11% and the balance essentially nickel, said alloy being characterized by high strength combined with an elongation of at least 25% and by a microstructure containing a dendritic phase having a eutectic structure within itself and part of said carbon as graphite in a nodular form.

2. A graphitic nickel alloy containing 1% to 2.5% carbon, 1.5% to 2% silicon, 1% to 1.5% manganese, sulfur up to 0.08%, magnesium in an amount exceeding the amount of sulfur present by 0.06% to 0.11% and the balance essentially nickel, said alloy being characterized by a microstructure containing part of said carbon as graphite in a nodular form and containinga dendritic phase having a eutectic structure within itself.

3. A graphitic nickel alloy containing 1% to 2.5% carbon, 1.5% to 2% silicon, 1% to 1.5% manganese, sulfur up to 0.08%, magnesium in an amount exceeding the amount of sulfur present by 0.04% to 0.17% and the balance cssentially nickel, said alloy being characterized by a tensile strength on the order of 55,000 pounds per square inch combined with an elongation of 20% or more and by a microstructure containing a dendritic phase having a eutectic structure within itself and part of said carbon as graphite in a nodular form.

4. A graphitic nickel alloy containing 1% to 2.5% carbon. 1.5% to 2% silicon, 1% to 1.5% manganese, sulfur in an amount which occurs in comparable graphitic nickel alloy products. magnesium in an amount exceeding the amount of sulfur present by 0.035% to 0.25% and the balance essentially nickel, said alloy being characterized by a tensile strength of at least 50,000 pounds per square inch combined with an elongation of at least 15% and by a microstructure containing a dendritic phase having a eutectic structure within itself and part of said carbon as graphite in a nodular form 5. A graphitic nickel alloy containing 0.8% to 3% carbon, 1% to 4% silicon, 0.5% to 4% manganese. sulfur in an amount characteristic of graphitic nickel casting alloys, magnesium in an amount exceeding the amount of sulfur present by 0.06% to 0.11% and the balance essentially nickel, said alloy being characterized by a microstructure containing part of said carbon as graphite in a nodular form and containing a dendritic phase having a eutectic structure within itself.

6. A graphitic nickel alloy containing 0.8% tr 3% carbon, 1% to 4% silicon, 0.5% to 4% manganese, sulfur up to at least 0.08%, magnesium in an amount exceeding the amount of sulfux present by 0.04% to 0.4% and the balance essentially nickel, said alloy being characterized by a tensile strength on the order of 55,000 pounds per square inch, by a microstructure containing the graphitic portion of said carbon substantially in a nodular form and containing a dendritic phase having a eutectic structure within itself.

7. A graphitic nickel alloy containing 0.8% to 3% carbon, 0.08% up to 0.45% of said carbon being combined carbon, 1% to 4% silicon, 0.5% to 4% manganese, sulfur up to at least 0.08% magnesium in an amount exceeding the amount of sulfur present by 0.045% to 0.17% and tht balance essentially nickel, said alloy containing the graphitic portion of said carbon substantially entirely in a nodular form and characterized by a microstructure containing a dendtritlig phase having a eutectic structure withir 1 se 8. A graphitic nickel alloy containin 0.8% u 3% carbon, 1% to 4% silicon, 0.5% to 4% manganese, sulfur up to 0.08%, magnesium in an amount exceeding the amount of sulfur present by 0.035% to 0.45% and the balance essentially nickel, said alloy in the as-cast condition having a tensile strength of at least 50,000 pounds per square inch and being characterized by a ,microstructure containing a dendritic phase having a eutectic structure Within itself and part of said carbon as graphite in a nodular form.

9. The method of producing a graphitic nickel alloy casting which comprises establishing a molten nickel bath containing 0.8% to 3% carbon and sulfur up to 0.08%, adjusting the bath temperature within the range of 2450 to 2850" F., introducing 0.5% to 4% manganese together with about one-half of the silicon required to produce a silicon content of 1% to 4% in the solidified casting, introducing magnesium in an amount exceeding the amount of sulfur present by 0.045% to 0.45%, introducing the remainder of the silicon required to produce a silicon con tent of 1% to 4% in the solidified casting and casting the bath to obtain a graphitic nickel alloy casting containing 0.8% to 3% carbon, sulfur up to 0.08%, 1% to 4% silicon, 0.5% to 4% manganese, magnesium exceeding the amount of sulfur present by 0.045% -to 0.45% and the balance essentially nickel, said alloy being characterized by a microstructure containing a dendritic phase having a eutectic structure within itself and part of said carbon as graphite in a nodular form.

10. In the founding of graphitic nickel alloys, the improvement which comprises establishing a nickel melt containing 1% to 2.5% carbon and sulfur in an amount which occurs in comparable graphitic nickel alloy produ'cts, adjusting the temperature of the melt to a suitable casting temperature. introducing into said nickel melt 1% to 1.5% manganese, together with about half of the silicon required to provide a silicon content of 1.5% to 2% in the solidified casting, thereafter introducing magnesium in an amount exceeding the amount of sulfur present by 0.06% to 0.11%, introducing as a final addition the remainder of the silicon required to provide a silicon content of 1.5% to 2% in the solidified casting, and casting said melt to obtain a graphitic nickel alloy having a microstructure containing part of said carbon as graphif; in a nodular form and containing a dendritic phase having a eutectic structure within itself.

11. In the founding of graphitic nickel alloys, the improvement which comprises establishing a nickel-carbon melt containing about 0.8% to 3% carbon and a small amount of sulfur characteristic of nickel-carbon alloy melts, introduc- 40 in; into said melt .5% to 47.6 m nganese and about half the silicon required to provide a silicon content of 1% to 4% in the solidified casting, thereafter introducing magnesium in an amount exceeding the amount of sulfur present by 0.04% to 0.4% and introducing into said melt the quantity of silicon required to provide a silicon content of 1% to 4% in the solidified casting, said quantity of silicon being 0.25% to 2.5% of said melt, and casting the melt to obtain a cast graphitic nickel alloy having a tensile strength on the order of 55,000 pounds per square inch and being characterized by a microstructure containing a dendritic phase having a eutectic structure within itself and part of said carbon as graphite in a nodular form.

GERALD LINFIELD LEE. JOHN 'I'RIMBLE EASH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Materials and Methods, Nov. 1946, page 1223.

Morrogh et al., treatise in Journal of The Iron and Steel Institute, London, England, March 1947, pages 357-359, 366, 367 (complete article pages 321-371).

Willings Press Guide, 1947, published by Willing's Press Service, Ltd, London, England; pag 1, 125, 

1. A GRAPHITIC NICKEL ALLOY CONTAINING 1% TO 2% CARBON, 1.5% TO 2% SILICON, 1% 1.5% MANGANESE, SULFUR UP TO 0.08%, MAGNESIUM IN AN AMOUNT EXCEEDING THE AMOUNT OF SULUR PRESENT BY 0.06% TO 0.11% AND THE BALANCE ESSENTIALLY NICKEL, SAID ALLOY BEING CHARACTERIZED BY HIGH STRENGTH COMBINED WITH AN ELONGATION OF AT LEAST 25% AND BY A MICROSTRUCTURE CONTAINING A DENDRITIC PHASE HAVING A EUTECTIC STRUCTURE WITHIN ITSELF AND PART OF SAID CARBON AS GRAPHITE IN A NODULAR FORM. 